The present invention generally relates to, for example, fuel delivery in internal combustion engines.
Internal combustion engines generate power by causing a mixture of air and combustible fuel, such as gasoline, to ignite and burn in one or more combustion chambers, such as combustion cylinders in an automobile. Conventionally, combustible fuel has been directed into the combustion chambers in a vapor form using either a carburetor or a fuel injector. Common fuel injectors are either continuous or pulsed. The continuous fuel injectors direct the combustible vapor into an intake manifold, and when an intake valve opens, the vapor is drawn into the combustion chamber by a piston. The pulsed fuel injectors direct fuel vapor on command into either a region upstream of each intake valve or directly into the combustion chambers. Both of these fuel delivery systems are highly developed, well known, and have been in use for decades.
In the internal combustion engine industry, it is an ongoing quest to achieve higher and higher fuel efficiency and to minimize harmful emissions into the atmosphere. To further both of these goals, one known approach is to use a gasoline/ethanol mixture as the fuel for the engine. The gasoline/ethanol mixture, which commonly comprise 90% gasoline and 10% ethanol, is created at oil refineries and injected into the vehicle combustion chambers with conventional fuel injectors. However, for a variety of reasons, including different evaporation rates and the relative stability of the respective mixture components, the gasoline/ethanol mixtures are generally not sufficiently precise by the time they reach the end consumer. As a result, some consumers that use a gasoline/ethanol mixture in their vehicles experience poor engine performance.
Another problem experienced by internal combustion engines that use conventional fuel injectors to direct fuel vapor into the combustion chambers is that they produce a relatively large amount of emissions during a cold start-up (i.e., start-up when the engine is at approximately ambient temperature). During operation of the engine at its normal operating temperature, it is desirable that average diameters of the fuel drops provided to the combustion chamber by the fuel injector be relatively large because the heat of the engine evaporates some of the fuel vapor. However, during a cold start-up, the relatively large fuel drops tend to condense on the cold metal wall of the combustion chamber (thereby remaining in liquid form). To ensure that sufficient fuel vapor exists in the combustion chamber to ignite, excess fuel is normally directed into the combustion chamber before or during a cold start-up. The excess fuel results in a certain amount of unburned fuel being expelled from the engine, which is undesirable.
The present invention relates to an improved fuel injector. In one embodiment of the invention, the fuel injector includes a first fluid input for receiving a first fluid; a second fluid input for receiving a second fluid; and a drop ejector configured to discretely eject fluid in a digital manner, wherein the drop ejector is further configured to receive the first and second fluids and to eject discrete droplets of the first fluid and discrete droplets of the second fluid. In another embodiment of the invention, the fuel injector includes a drop ejector configured to discretely eject fluid in a digital manner, wherein the drop ejector includes a first set of firing chambers and a second set of firing chambers, wherein each firing chamber of the first set has a first volume, and wherein each firing chamber of the second set has a second volume.